The oil-based blue inks heretofore used comprise predominantly a metal complex salt dye in view of hue and durability. In particular, a copper phthalocyanine-based dye is almost an essential component as a metal complex salt dye. However, the metal complex salt dye has a problem in the solubility in an oily solvent. Furthermore, use of a metal complex salt dye alone is disadvantageous in that the concealing property is low. Accordingly, in the case of using the metal complex salt dye, a triarylmethane-based dye of giving good coloration is used in combination in many cases to adjust the hue. As such, in the ink compositions, the metal complex salt dye is used by mixing it with various other raw materials or a solvent. However, the metal complex salt dye is poor in solubility, and particularly in compatibility, and, depending on the solvent or raw materials used and the amount added thereof, there arise troubles, such as an extreme increase in the ink viscosity or generation of precipitates.
In some cases, a pigment dispersion is used in place of the metal complex salt dye so as to impart durability. However, the pigment originally has no solubility and no compatibility and, therefore, when the pigment is used in combination with other materials, there often arise troubles such as thickening or generation of precipitates, similar to the case of using a metal complex salt dye.
By taking account of the above-described problems in conventional techniques, the object of the present invention is to provide an oil-based ink composition which, on use of a non-aqueous (oily) solvent over a wide range, particularly an alcohol such as an alcohol having 2 or more carbon atoms or a polyhydric alcohol, or an ether represented by glycol ether, enables addition of a blue-type dye to a high concentration to overcome those problems encountered under high-concentration conditions, and exhibits good compatibility with other raw materials in the ink and excellent low-temperature aging stability. Also, the object of the present invention is to prevent occurrence of decoloration by alcohols.